Scroll-type fluid compressors are well known in the prior art. U.S. Pat. No. 4,432,708 issued to Hiraga et al discloses an apparatus including two scrolls, each having a circular end plate and a spiral element disposed on each plate. The scrolls are radially offset such that both spiral elements cooperate to make a plurality of contacts between their spiral curved surfaces.
In operation, one of the scrolls is subjected to an orbital motion and the line contacts shift, resulting in a change in the volume of the fluid pockets contained within the scrolls. This change in volume of the fluid pockets is utilized to compress fluids, for example air conditioning fluids needed for operation of the air conditioning system of automobiles.
Prior art compressors such as disclosed in U.S. Pat. No. 4,604,039 to Terauchi and U.S. Pat. No. 4,890,987 to Sato et al include a main drive shaft supported by a main drive shaft bearing. The main drive shaft bearing is comprised of a bearing race and two spaced sets of bearings surrounding the circumference of the main drive shaft. The nose portion of the front cover of the compressor extends around and encloses the outer periphery of the main bearings. A clutch bearing is disposed directly on the outer diameter of the nose portion of the compressor.
The clutch bearing supports the clutch assembly used to induce and control the rotational motion needed to operate the compressor. The compressors disclosed in the Terauchi patent and the Sato et al patent are representative of prior art designs utilizing a dual bearing assembly for rotatably supporting both the main drive shaft and the clutch assembly. Both designs disclose a nose portion located intermediate the clutch bearing and the main drive shaft bearing. It is known in the art that this nose portion is difficult and relatively expensive to machine to rigid dimensional specifications. The precision machining of the nose portion adds expense to the manufacture of the overall compressor.
The main drive shaft bearing and outer pulley bearing in combination with the nose portion of the front cover also create an axial "stack up" of dimensional tolerances. This axial "stack-up" is the cumulative addition of dimensional tolerances of adjacent parts. This cumulative addition causes premature failure of the compressor components and drive belts.
The clutch assembly includes a rotor which rests on the clutch bearing and cooperates with an engagement hub assembly to comprise the main clutch assembly components needed for the compressor's operation. In use, when air conditioning is required inside the automobile the clutch assembly is energized by a switch in the passenger compartment. The clutch assembly is energized and an electromagnet in the clutch assembly creates a magnetic field pulling the engagement hub assembly toward the rotor. The engagement hub assembly and rotor engage and induce rotational movement in the main drive shaft. Eccentric mounting of a drive pin on a disc rotor associated with the main drive shaft induces orbital motion in the scroll., When the air conditioning system is not operating, the engagement hub assembly and rotor are not engaged and the rotor rotates independently from the engagement hub assembly.
Generally, wear occurs between the engagement hub assembly and rotor due to normal operating contact between the engagement hub assembly and rotor. If axial "stack ups" between the main bearing, nose portion and clutch bearing reach a high level, premature wear of the engagement hub assembly, rotor and other compressor components occurs. Axial stack-up also contributes to drive belt misalignment which greatly increases drive belt wear. If axial "stack-up" reaches a critical level, clutch engagement will not occur.
Precise relative positioning of interfacing components is a prerequisite to an acceptable compressor design. Relative parallel positioning or "squareness" as it is sometimes termed is essential for operation of the engagement hub assembly and rotor in the clutch assembly. Axial tolerance "stack up" alters the desired positional relationships and may cause premature wear because of contact between misaligned components. Specifically, any misalignment of the engagement hub assembly and rotor forces one portion of the engagement hub assembly to contact the rotor before the other portion, creating premature wear areas that lead to component failure. This condition decreases the overall life of the engagement hub assembly and rotor and consequently the overall life of the air conditioning compressor in general. Misalignment of the engagement hub assembly and rotor also heightens noise levels and vibration created by the clutch assembly during engagement.
The bearing assembly disclosed in U.S. Pat. No. 4,673,340 to Mabe et al patent depicts a main drive shaft bearing utilizing only one bearing assembly. The pulley bearing disclosed is similar to those disclosed in the Sato et al patent and the Terauchi patent. Again, a machined nose portion extends between the main drive shaft bearing and the pulley bearing. U.S. Pat. No. 4,432,708 to Hiraga et al discussed above discloses yet a third type of bearing assembly. A first bearing is used to support the main drive shaft. This bearing is located on an oversized journal disposed adjacent, but not between, the outer pulley bearing. The design of the nose portion requires machining of both inner and outer dimensions to fit and support the bearing assembly in operation.